World’s Biggest Sand Battery Begins Operation in Finland

Finnish startup Polar Night Energy has commissioned the world’s largest sand battery in Pornainen, in collaboration with the local district heating provider, Loviisan Lämpö.

Towering nearly 13 metres high and 15 metres wide, the sand battery uses around 2,000 tonnes of crushed soapstone to store thermal energy. With a 1 MW heat output and 100 MWh storage capacity, it dwarfs the company’s first commercial installation in Kankaanpää launched in 2022 — now standing at ten times the scale.

The battery is now the primary heat source for Pornainen’s district heating network. During summer, it can meet the town’s heating demand for almost a month. In winter, it can sustain it for about a week. The impact on emissions is equally impressive. 

Annual carbon dioxide equivalent emissions from the local heating system are expected to drop by 160 tonnes,  nearly 70 percent. This will enable the complete phaseout of oil and cutting wood chip usage in the Pornainen’s heating network by 60 percent.

“This is a major step toward our goal of becoming climate neutral by 2035,” said Mikko Paajanen, CEO of Loviisan Lämpö.

The project was first unveiled in early 2024, with construction engaging over 100 workers and 40 subcontractors. It reached its operational phase after successful testing began in November 2024.

 

This is Just a Beginning

Polar Night Energy sees this as just the beginning with the firm aiming to go climate neutral by 2035. 

“This is a solid foundation for scaling sand battery technology to larger capacities and new industries,” said Liisa Naskali, COO of the company. Talks are already underway with both Finnish and international partners for future deployments.

Sand batteries do not use chemicals. They don’t contain rare earth metals or moving parts. This makes them cheaper to maintain and safer for the environment. A Sand Battery is a high-temperature thermal energy storage technology that stores clean and affordable electricity as heat in sand or similar solid materials. It can be used to produce heat for both district heating networks and a wide range of industrial processes.

Looking ahead, the company is also planning a pilot facility in southern Finland to explore converting thermal energy back into electricity — a promising next step in sustainable power storage. Backed by €7.6 million in seed funding, Polar Night Energy is positioning sand as a serious contender in the clean energy transition.